The subject of endoprosthetic joints has received a great deal of attention over the past several years and has particularly received much attention in recent years due in part to the availability of improved materials inert to human or animal bodies and to improved techniques for manipulating same. However, in spite of such intensive study, the endoprosthetic joints previously available, while in many cases satisfactory to a limited degree, are far from fully satisfactory and intensive work is continuing for the further improvement of such endoprostheses.
One particular area which has been extensively studied relates to the endoprosthetic joints used to replace the digital (i.e. finger and thumb) joints. While many such prosthetic joints have been developed for this purpose, and while many of these joints have been observed to perform with varying degrees of success, nevertheless one common problem encountered with most endoprosthetic joints relates to the inability to successfully hold the ligaments and tendons of the digit in proper position around the joint. A finger has what is commonly called the "volar plate." This plate, which includes the tendons and ligaments of the finger, forms a layer positioned adjacent the bottom of the joint. When the natural joint is replaced by an endoprosthetic joint, this volar plate is no longer attached to the joint and is thus not secured in its normal position. This volar plate thus has a tendency to become displaced, as by sliding sidewardly with respect to the joint, which in turn seriously affects both the appearance and the desired natural manipulation of the finger. This displacement of the volar plate causes an imbalance in the tendons as the finger is flexed, whereby proper pivoting movement of the finger and the return thereof into a straight position is seriously affected.
Accordingly, it is an object of the present invention to provide an improved endoprosthesis for a digital joint, and particularly a finger, including knuckle, joint, which can successfully overcome the above-mentioned problem so that a digit having the endoprosthetic joint implanted therein will have a natural appearance and be capable of natural movement.
More specifically, it is an object of this invention to provide an improved endoprosthetic joint, as aforesaid, which is particularly suitable for the finger joint between the phalangeal and metacarpal bones and includes head and socket members which can be easily implanted into the bone structure on either side of the joint, with the head and socket members being suitably snapped together. The endoprosthetic joint of this invention is provided with suitable structure associated with the socket member, such as external webs, which permit the ligaments, muscles and/or tendons to be sutured to the implanted joint substantially on diametrically opposite sides thereof so that they are maintained in the desired position. This thus permits a natural pivotal movement of the digit while at the same time maintaining a proper balance on the muscles, tendons and ligaments.